A typical color ink jet print head includes an array of ink jets that are closely spaced from one another for use in ejecting drops of ink toward a receiving surface. The typical print head also has at least four ink manifolds for receiving the black, cyan, magenta and yellow ink used in monochrome plus subtractive color printing. The number of such manifolds may be varied where a printer is designed to print solely in black ink, gray scale or with less than a full range of color.
In a conventional ink jet print head, each ink jet is paired with an electromechanical transducer, such as a piezoelectric transducer (PZT). The transducer is bonded to the flexible diaphragm and typically has metal film layers to which an electronic transducer driver is electrically connected. When a voltage is applied across the metal film layers of the transducer, the transducer attempts to change its dimensions. Because it is rigidly attached to a flexible diaphragm, the transducer bends and deforms the diaphragm, thereby causing the outward flow of ink through the ink jet.
It has been discovered that firing multiple transducers simultaneously at particular frequencies can create a global mechanical vibration mode in the print head. For example, where the ink jet nozzles are arrayed horizontally in an extended rectangular formation across the print head (see FIG. 5), firing multiple transducers at a particular frequency cam create a vertical vibration mode and bending about a horizontal axis A of the print head. A given print head may also have one or more resonance modes that correspond to a particular frequency or firing rate of the transducers/ink jets. As more transducers are actuated simultaneously at a resonant frequency, the magnitude of the mechanical vibration within the print head increases. This vibration may cause jets to become less efficient and slower in operating, especially in certain regions of the print head that are more sensitive to vibration. This reduction in jet efficiency can lead to ink drop position errors on the receiving surface and visible image artifacts, such as banding.
U.S. Pat. No. 5,781,212 to Burr et al. discloses a print head structure that controls acoustic or fluidic pressure waves in the ink flow passageways by utilizing a baffle structure to dampen the pressure waves within the passageways. U.S. Pat. No. 4,730,197 to Raman et al. teaches the use of compliance relief slots adjacent to a portion of a compliance plate that forms the bottoms of ink manifolds. The slots allow the compliance plate to flex in response to ink pressure changes and fluidic pressure waves in the manifolds. Neither of these print head structures addresses the problem of global mechanical vibrations created by simultaneously firing multiple ink jets.
Accordingly, a need exists for an improved ink jet print head that dampens global mechanical vibrations created by simultaneously firing multiple ink jets.